We wish to study why the haploid DNA content of higher organisms is so large, whether their nominally "repeated" DNA sequences function because of sequence similarity, and sequence rearrangement in the evolution of the eukaryotic genome. If repeated sequences function in a manner that requires similarity of sequence (e.g. in gene regulation during development), and if the parameters of sequence arrangement (the "sequence organization") are important to genome function, then we would expect species within a genus to have a closely similar sequence organization despite a variation in haploid nuclear DNA content. If these species show quite a different sequence arrangement, then the fundamental importance of sequence organization is not supported and the repeats may function in a sequence-independant manner. We propose to determine repeat sequence length and arrangement in the genus Vicia (possibly also Crepis) which contains species varying by at least six-fold in haploid DNA content. We have discovered what may be a precursor-product relationship between satellite DNA (clustered repeated sequences) and dispersed repeated sequences in one family of plants that we interpret as evidence for an amplification-translocation mechanism of genome growth during evolution. We propose to examine this relationship in more detail in this and other families of plants. Some satellite DNA is also linked to ribosomal RNA genes of melon and squash and we propose to investigate the strikingly different linkage arrangements in these closely related species for possible insertion and/or unusual spacer sequences. Our evidence suggests that the fundamental changes in the chloroplast genome during angiosperm evolution involved the rearrangement of a core of conserved sequences with respect to the more rapidly changing sequences. We propose to use heteroduplex analysis and blot-hybridization to further study chloroplast DNA sequence rearrangement in evolution.